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Abstract:

In a silent chain transmission, noise performance is improved by
preventing guide plates of a silent chain from contacting sprocket teeth
before the link plates of the chain contact the sprocket teeth. The
silent chain transmission comprises a silent chain in engagement with a
sprocket. The silent chain comprises guide rows, each having a pair of
guide plates and a plurality of middle link plates, and non-guide rows,
each having a plurality of inner link plates. An engagement starting
point of the middle link plate with a sprocket tooth and an engagement
starting point of the inner link plate with the sprocket tooth are set at
positions such that the guide plate is prevented from contacting the
sprocket tooth before the respective link plates start to engage the
sprocket tooth when runout of the chain in the direction of its width
occurs.

Claims:

1. A silent chain transmission system comprising a silent chain having
guide rows each having a pair of guide plates and middle link plates
disposed between said pair of guide plates, non-guide rows each having a
plurality of inner link plates and pairs of link pins each held by said
pair of guide plates by being separated in a chain traveling direction,
wherein said guide rows and said non-guide rows being alternately in mesh
in the chain traveling direction by being linked by the pairs of link
pins, and sprockets having sprocket teeth with which said silent chain is
engageable, characterized in that an engagement starting point of at
least one of link plates of said middle link plate and said inner link
plate with the sprocket tooth is set at position of avoiding said guide
plate from contacting with said sprocket tooth before one of said link
plates starts to engage with said sprocket tooth when said silent chain
is in a transverse-runout state.

2. The silent chain transmission system according to claim 1,
characterized in that said guide plate has a shape of avoiding said guide
plate from contacting with said sprocket tooth before one of said link
plates starts to engage with said sprocket tooth in said
transverse-runout state.

3. The silent chain transmission system according to claim 1,
characterized in that when one of said link plates is said middle link
plate, said guide plate has a shape of avoiding said guide plate from
contacting with said sprocket tooth before an inner-flank surface of said
middle link plates starts to engage with said sprocket tooth in said
transverse-runout state.

4. The silent chain transmission system according to claim 1,
characterized in that when one of said link plates is said inner link
plate, said guide plate has a shape of avoiding said guide plate from
contacting with said sprocket tooth before an inner-flank surface of said
inner link plates starts to engage with said sprocket tooth in said
transverse-runout state.

5. The silent chain transmission system according to any one of claim 4,
characterized in that said guide plate has a shape of avoiding said guide
plate from contacting with said sprocket tooth during a period from when
said inner-flank surface of said inner link plate starts to engage with
said sprocket tooth until when an outer-flank surface of said middle link
plate seats on the sprocket in said transverse-runout state.

Description:

FIELD OF THE INVENTION

[0001] The present invention relates to a silent chain transmission system
comprising a silent chain having guide plates and sprockets with which
the silent chain engages. The silent chain transmission system is for use
in automobiles, e.g., a timing chain system of an internal combustion
engine, industrial machines and the like.

BACKGROUND ART

[0002] Among the silent chain transmission systems having a silent chain
and sprockets, there has been known one in which the silent chain has
guide rows each having a pair of guide plates and middle link plates
disposed between the pair of guide plates, non-guide rows each having a
plurality of inner link plates and pairs of link pins each provided
through the pair of guide plates, wherein the guide rows and the
non-guide rows are in mesh alternately in a chain traveling direction by
being linked by the pairs of link pins (see Patent Document 1 for
example).

PRIOR ART DOCUMENT

Patent Document

[0003][Patent Document 1] Japanese Patent No. 3054144

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

[0004] When the silent chain transmission system is in operation, a
traveling state of the silent chain changes variously and there is a case
when the silent chain causes runout in a chain width direction (referred
to as "transverse-runout" hereinafter) for example.

[0005] Then, as shown in FIG. 5, when the silent chain 01 has guide rows
02 each having a pair of guide plates 03 and a plurality of middle link
plates 04, non-guide rows 05 having a plurality of inner link plates 06
and pairs of link pins 07 each provided through the pair of guide plates
03 and when the guide row 02 starts to engage with a driving sprocket 08,
there is a case when the guide plate 03 contacts with the sprocket tooth
09 before the middle link plate 04 contacts with the sprocket tooth 09
when the transverse runout described above occurs when an inner end
surface 03a of an inner outline face of the guide plate 03 is located in
a vicinity of an engagement starting point 04p with the sprocket tooth 09
on an inner-flank surface 04a of the middle link plate 04.

[0006] Further, as shown in FIG. 6, when an inner side end surface 03b of
the inner outline face of the guide plate projects toward the sprocket
tooth 09 more than the engagement starting point 06p with the sprocket
tooth 09 on an inner-flank surface 06a of the inner link plate 06 and
when the non-guide row 05 starts to engage with the driving sprocket 08,
there is a case when the guide plate 03 contacts with the sprocket tooth
09 before the inner link plate 06 contacts with the sprocket tooth 09.

[0007] Even though the sprocket teeth are originally designed to start to
contact and engage with the middle link plates and inner link plates
without contacting the guide plates when the silent chain starts to
engage with the sprocket to reduce noise of the chain, the silent chain
causes noise due to the contact of the guide plates with the sprocket
teeth and drops noise performance of the silent chain transmission system
if the sprocket teeth contact with the guide plates prior to the middle
and inner link plates.

[0008] Accordingly, the present invention aims at solving the
aforementioned prior art problems by providing a silent chain
transmission system whose noise performance is improved by preventing
guide plates of a silent chain from contacting with sprocket teeth prior
to link plates.

[0009] The invention also aims at realizing the abovementioned object with
a simple structure by arranging a shape of the guide plate.

Means for Solving the Problems

[0010] In order to solve the aforementioned problems, according to the
invention described in claim 1, there is provided a silent chain
transmission system comprising a silent chain (2) having guide rows (3)
each having a pair of guide plates (10) and middle link plates (30)
disposed between the pair of guide plates (10), non-guide rows (4) each
having a plurality of inner link plates (40), pairs of link pins (5) each
held by the pair of guide plates (10) by being separated in a chain
traveling direction, wherein the guide rows (3) and the non-guide rows
(4) being alternately in mesh in the chain traveling direction by being
linked by the pairs of link plates (5), and sprockets (7) having a
plurality of sprocket teeth (8) with which the silent chain is
engageable, wherein an engagement starting point (P3, P4) of at least one
of link plates (30, 40) of the middle link plate (30) and the inner link
plate (40) with the sprocket tooth (8) is set at position of avoiding the
guide plate (10) from contacting with the sprocket tooth (8) before one
of the link plates (30, 40) starts to engage with the sprocket tooth (8)
when the silent chain (2) is in a transverse-runout state.

[0011] According to the invention described in claim 2, the guide plate
(10) has a shape of avoiding the guide plate (10) from contacting with
the sprocket tooth (8) before one of the link plates (30, 40) starts to
engage with the sprocket tooth (8) in the transverse-runout state.

[0012] According to the invention described in claim 3, when one of the
link plates (30, 40) is the middle link plate (30), the guide plate (10)
has a shape of avoiding the guide plate (10) from contacting with the
sprocket tooth (8) before an inner-flank surface (34, 35) of the middle
link plate (30) starts to engage with the sprocket tooth (8) in the
transverse-runout state.

[0013] According to the invention described in claim 4, when one of the
link plates (30, 40) is the inner link plate (40), the guide plate (10)
has a shape of avoiding the guide plate (10) from contacting with the
sprocket tooth (8) before an inner-flank surface (44, 45) of the inner
link plate (40) starts to engage with the sprocket tooth (8) in the
transverse-runout state.

[0014] According to the invention described in claim 5, the guide plate
(10) has a shape of avoiding the guide plate (10) from contacting with
the sprocket tooth (8) during a period from when the inner-flank surface
(44, 45) of the inner link plate (40) starts to engage with the sprocket
tooth (8) until when an outer-flank surface (36, 37) of the middle link
plate (30) seats on the sprocket (7) in the transverse-runout state.

Advantageous Effects of the Invention

[0015] According to the invention described in claim 1, because the
engagement starting point of one of the link plates of the silent chain
with the sprocket tooth is set at the position of avoiding the guide
plate from contacting with the sprocket tooth before one of the link
plates starts to engage with the sprocket tooth when the silent chain is
in a transverse-runout state, it is possible to prevent the sprocket
tooth from contacting with the guide plate until when the flank surface
of one of the link plates starts to engage with the sprocket tooth when
the traveling silent chain starts to engage with the sprocket tooth in
the transverse-runout state.

[0016] As a result, it is possible to prevent the guide plate 10 from
contacting with the sprocket tooth 8 even when the silent chain 2 is in
the transverse-runout state before and after when the silent chain 2
starts to engage with the sprocket tooth 8. Then, it becomes possible to
keep the original engagement starting configuration of the sprocket tooth
8 that conforms to such a design concept that the respective link plates
30 and 40 of the silent chain 2 contact first with the sprocket tooth 8
in the same manner when the silent chain 2 travels on the normal position
and to improve the noise performance of the silent chain transmission
system 1 because it becomes possible to prevent the noise otherwise
caused by the contact of the guide plate 10 with the sprocket tooth 8
before starting the engagement.

[0017] According to the invention described in claim 2, the following
effect is brought about in addition to the effects of the invention
described in claim 1.

[0018] That is, it is possible to realize the setting of the engagement
starting point of one of the link plates with the sprocket tooth at the
position of avoiding the guide plate from contacting with the sprocket
tooth before one of the link plates starts to engage with the sprocket
tooth in the transverse-runout state by the simple structure by using the
guide plate having the shape of avoiding the guide plate from contacting
with the sprocket tooth before one of link plates starts to engage with
the sprocket tooth.

[0019] According to the invention described in claim 3, the following
effect is brought about in addition to the effects of the invention
described in claim 1.

[0020] That is, it is possible to realize the setting of the engagement
starting point of inner-flank surface of the middle link plate with the
sprocket tooth at the position of avoiding the guide plate from
contacting with the sprocket tooth before the inner-flank surface starts
to engage with the sprocket tooth in the transverse-runout state by a
simple structure by using the guide plate having the shape of avoiding
the guide plate from contacting with the sprocket tooth before the
inner-flank surface starts to engage with the sprocket tooth.

[0021] According to the invention described in claim 4, the following
effect is brought about in addition to the effects of the invention
described in claim 1.

[0022] That is, it is possible to realize the setting of the engagement
starting point of inner-flank surface of the inner link plate with the
sprocket tooth at the position of avoiding the guide plate from
contacting with the sprocket tooth before the inner-flank surface starts
to engage with the sprocket tooth in the transverse-runout state by the
simple structure by using the guide plate having the shape of avoiding
the guide plate from contacting with the sprocket tooth before the
inner-flank surface starts to engage with the sprocket tooth.

[0023] According to the invention described in claim 5, the following
effect is brought about in addition to the effect of the invention
described in claim 4.

[0024] That is, the guide plate does not contact with the sprocket tooth
even after when the inner-flank surface of the inner link plate starts to
engage with the sprocket tooth until when the outer-flank surface of the
middle link plate seats on the sprocket in the transverse-runout state in
the same manner with the start of engagement of the inner-flank surface
of the inner link plate and the sprocket tooth. As a result, because it
becomes possible to prevent noise otherwise caused by the contact of the
guide plate with the sprocket tooth, it is possible to improve the noise
performance of the silent chain transmission system further.

[0025] Still more, it is possible to realize the non-contact state of the
guide plate 10 and the sprocket tooth 8 during the period after when the
inner link plate starts to engage with the sprocket 7 until when the
middle link plate 30 seats on the sprocket 7 by the simple structure by
using the guide plate 10 having the shape of avoiding the guide plate 10
from contacting with the sprocket tooth 8 during the period after when
the inner link plate 40 starts to engage with the sprocket 7 until when
the middle link plate 30 seats on the sprocket 7.

BRIEF DESCRIPTION OF DRAWINGS

[0026]FIG. 1 is a side view showing a main part of a silent chain
transmission system of an embodiment of the invention.

[0027] FIG. 2 is a section view of the main part taken at a plane
including a center line of rotation and along a chain traveling direction
of a silent chain in the silent chain transmission system in FIG. 1.

[0028] FIG. 3 is a diagram around a guide row of the silent chain in the
silent chain transmission system shown in FIG. 1, wherein FIG. 3(a) is an
enlarged side view of the main part and FIG. 3(b) is a section view taken
along arrows b-b in FIG. 3(a).

[0029]FIG. 4 is an enlarged side view of the main part around a non-guide
row of the silent chain in the silent chain transmission system in FIG.
1.

[0030]FIG. 5 is an enlarged side view of a main part around a guide row
of a silent chain in a prior art silent chain transmission system.

[0031]FIG. 6 is an enlarged side view of a main part around a non-guide
row of the silent chain in the silent chain transmission system in FIG.
5.

PREFERRED EMBODIMENT OF THE INVENTION

[0032] The specific mode of a silent chain transmission system of the
present invention may take any configuration as long as the silent chain
transmission system comprises a silent chain having guide rows each
having a pair of guide plates and middle link plates disposed between the
pair of guide plates, non-guide rows each having a plurality of inner
link plates and pairs of link pins each held by the pair of guide plates
by being separated in a chain traveling direction, wherein the guide rows
and the non-guide rows being alternately in mesh in the chain traveling
direction by being linked by the pair of link plates, and sprockets
having sprocket teeth with which the silent chain is engageable,

[0033] wherein an engagement starting point of at least one of link plates
of the middle link plate and the inner link plate with the sprocket tooth
is set at position of avoiding the guide plate from contacting with the
sprocket tooth before one of the link plates starts to engage with the
sprocket tooth when the silent chain is in a transverse-runout state, and

[0034] which prevents the guide plate of the silent chain from contacting
with the sprocket tooth prior to the link plates and improves noise
performance of the silent chain transmission system.

[0035] For instance, the sprocket tooth may be formed into a shape of
avoiding the guide plate from contacting with the sprocket tooth before
one of the link plates starts to engage with the sprocket tooth, beside
the shape of the guide plate, in order to set the engagement starting
point of one of the link plates with the sprocket tooth at position of
avoiding the guide plate from contacting with the sprocket tooth before
one of the link plates starts to engage with the sprocket tooth.

[0036] Still more, the silent chain may be an outer flank engaging and
outer flank seating type silent chain or an inner flank engaging and
inner flank seating type silent chain for example other than the inner
flank engaging and outer flank seating type silent chain.

[0037] The silent chain may be also either an endless chain or a
reciprocating end-cut chain.

[0038] The sprocket may be either a driving sprocket or a driven sprocket.

Embodiment

[0039] An embodiment of the invention will be explained below with
reference to FIGS. 1 through 4.

[0040] Here, FIG. 1 is a side view showing a main part of a silent chain
transmission system 1 of an embodiment of the invention, FIG. 2 is a
section view showing the main part of the silent chain transmission
system 1 in FIG. 1, FIG. 3 is a diagram around a guide row 3 of a silent
chain 2, wherein FIG. 3(a) is an enlarged side view of the main part and
FIG. 3(b) is a section view taken along arrows b-b in FIG. 3(a) and FIG.
4 is an enlarged side view of the main part around a non-guide row 4 of
the silent chain 2.

[0041] As shown in FIGS. 1 and 2, the silent chain transmission system 1
comprises the silent chain 2 in which a plurality of guide rows 3 and a
plurality of non-guide rows 4 are alternately in mesh in a chain
traveling direction by being flexibly linked by a plurality of link pins
5 and a sprocket structure 6 having one or more sprockets around which
the silent chain 2 is wrapped.

[0042] The sprocket has a plurality of sprocket teeth with which the
silent chain 2 is engageable.

[0043] The silent chain 2 is an endless chain in which the guide rows 3
and the non-guide rows 4 are endlessly linked by the link pins 5 in the
present embodiment.

[0044] The sprocket structure 6 is composed of a plurality of sprockets,
i.e., more specifically, one or more driving sprockets and one or more
driven sprockets, in the present embodiment.

[0045] As one example of the sprocket, FIG. 1 shows a sprocket 7 which is
a driving sprocket having a plurality of sprocket teeth 8 and which
rotates in a rotational direction R centering on a center line of
rotation Ls.

[0046] Here, the chain traveling direction is a direction in which the
silent chain 2 engaging with the sprocket 7 moves and a chain width
direction is a direction in parallel with a center line of flection Lc of
the guide and non-guide rows 3 and 4 or with the center line of rotation
Ls of the sprocket 7 specified by the link pins 5. Front and rear
directions refer to forward and rearward directions of the chain
traveling direction.

[0047] A side view refers to viewing from a direction in parallel with the
center line of rotation Ls and a radial direction is a radial direction
centering on the center line of rotation Ls of the sprocket 7.

[0048] Still more, a transverse-runout state of the silent chain 2 means a
state in which the traveling silent chain 2 runs out in the chain width
direction.

[0049] The silent chain 2 has the guide rows 3 each having a pair of guide
plates 10 and one or more or a first predetermined number of, i.e., four
middle link plates 30 here, the non-guide rows 4 each having one or more
or a second predetermined number greater than the first predetermined
number by one, i.e., five inner link plates 40 here, and pairs of link
pins 5 each held by the pair of guide plates 10 per one guide row 3,
separated in the chain traveling direction and rotably link the middle
link plates 30 and the inner link plates 40.

[0050] In each guide row 3, the plurality of middle link plates 30 is
disposed between the pair of guide plates 10 in the chain width
direction. Each guide plate 10 is provided with pin holding holes 11 as a
pair of holing portions for holding the pair of link pins 5 at positions
separated in the chain traveling direction (or in the front-rear
direction).

[0051] Both ends in the chain traveling direction of each link plate 5 are
fixed to the guide plates 10 by fixing means, e.g., press-fitting or
caulking, while being inserted into the pin holding holes 11.

[0052] In each non-guide row 4, the plurality of inner link plates 40 is
disposed between the pair of guide plates 10 in the chain width direction
while straddling over the guide rows 3 neighboring in the chain traveling
direction.

[0053] Then, the first predetermined number of middle link plates 30 and
the second predetermined number of inner link plates 40 are disposed
while being alternately layered in the chain width direction between the
pair of guide plates 10.

[0054] Each of the middle link plates 30 and each of the inner link plates
40 have a pair of link teeth 32 and 33 and 42 and 42, respectively, that
project inwardly in the radial direction and that engage or contact with
the sprocket tooth 8 as shown also in FIGS. 3 and 4.

[0055] The pair of link teeth 32 and 33 is composed of a front link tooth
32 on the front side and a rear link tooth 33 on the rear side in terms
of the chain traveling direction and the pair of link teeth 42 and 43 is
composed of a front link tooth 42 on the front side and a rear link tooth
43 on the rear side in terms of the chain traveling direction.

[0056] The respective link teeth 32 and 33 have inner-flank surfaces 34
and 35, contactable with the sprocket teeth 8, and outer-flank surfaces
36 and 37 and the respective link teeth 42 and 43 have inner-flank
surfaces and 45, contactable with the sprocket teeth 8, and outer-flank
surfaces 46 and 47.

[0057] The pairs of the inner-flank surface 34 and 35 and 44 and 45 of the
respective link plates 30 and 40 are composed of the front inner-flank
surfaces 34 and 44 on the front side and the rear inner-flank surfaces 35
and on the rear side in terms of the chain traveling direction.
Similarly, the pairs of the outer-flank surface 36 and 37 and 46 and 47
are composed of the front outer-flank surfaces 36 and 46 on the front
side and the rear outer-flank surfaces 37 and 47 on the rear side in
terms of the chain traveling direction.

[0058] The middle and inner link plates 30 and 40 are provided with pin
inserting holes 31 and 41 (see FIG. 2) through which the link pins 5 are
inserted respectively at positions separated in the chain traveling
direction.

[0059] The pair of link pins 5 held by the pair of guide plates 10 in each
guide row 3 links a group of link plates composed of the middle and inner
link plates 30 and 40 while penetrating through the pin inserting holes
31 and 41 between the pair of guide plates 10.

[0060] The middle and inner link plates 30 and 40 are turnable or flexible
centering on the center line of rotation which is also the center line of
flection Lc specified by the link pin 5 while being linked by the link
pins 5.

[0061] While the link pin 5 is a single round pin in the present
embodiment, it may be a rocker pin having a plurality of pins.

[0062] When the guide rows 3 and non-guide rows 4 engage with the sprocket
teeth 8 when the silent chain 2 travels at normal position (referred to
as `normal position` hereinafter) as shown in FIGS. 4 and 5, the
engagement starts as the front inner-flank surfaces 34 and 44 of the
respective link plates 30 and 40 contact with the sprocket teeth 8. Then,
in a process in which engagement starting points move inwardly in the
radial direction along the sprocket tooth 8 with the advance of this
engagement, the engagement starting points on the respective link plates
30 and 40 shift from the inner-flank surfaces 34 and 44 to the respective
pairs of outer-flank surfaces 36 and 37 and 46 and 47. When the
engagement ends, the both outer-flank surface 36 and 37 and 46 and 47 of
the respective link plates 30 and 40 contact with the sprocket teeth 8
and the middle link plates 30 seat on the sprocket 7. Accordingly, the
silent chain 2 is a so-called inner-flank engaging and outer-flank
seating type chain.

[0063] Here, the normal position is a position when the sprocket tooth 8
is located within a distance W in the chain width direction (see FIG. 2)
between the pair of guide plates 10 per guide row 3. In other words, it
is a position in which the guide plates 10 and the sprocket tooth 8 are
not located at the same position in the chain width direction, i.e., do
not overlap at the position in the chain width direction.

[0064] When the silent chain 2 is in the transverse-runout state, it means
that the silent chain 2 moves relatively in the chain width direction
from the normal position and is not located at the normal position.

[0065] Therefore, when the silent chain 2 is in the transverse-runout
state, the silent chain 2 moves relatively in the chain width direction
from the normal position and the guide plates 10 are not located within
the distance W, i.e., are in a state of moving relatively in the width
direction.

[0066] It is noted that FIGS. 1 through 4 illustrate the silent chain 2
located at the normal position.

[0067] As shown in FIG. 2, each guide plate 10 has an outer side surface
12 and an inner side surface 13 (see also FIG. 3) which are side surfaces
in the chain width direction.

[0068] Still more, as shown in FIGS. 3(a) and 4, an outline face 20 of the
guide plate 10 in the side view can be divided into an inner outline face
22 on the side where the sprocket tooth 8 is located (i.e., radially
inside) and an outer outline face 21 on the side opposite from the inner
outline face 22 (i.e., radially outside) by a border of a maximum width
portion 15 having a maximum width in the chain traveling direction in the
guide plate 10. Then, the inner outline face 22 has an inner end surface
23 having a portion located most inwardly in the radial direction within
the inner outline face 22 and a pair of inner side end surfaces 24 and 25
from the inner end surface 23 to the maximum width portion 15.

[0069] In the side view, the inner end surface 23 is a portion where
intersecting portions 22a and 22b of the inner outline face 22 and the
pair of inner-flank surfaces 44 and 45 of the middle link plate 30 or
vicinities of the intersecting portions 22a and 22b become both end
portions thereof in the chain traveling direction, and is located
inwardly in the radial direction more than the pair of inner side end
surfaces 24 and 25.

[0070] The pair of inner side end surfaces 24 and 25 is, in terms of the
chain traveling direction, the front inner side end surface 24 on the
front side and the rear inner side end surface 25 on the rear side.

[0071] Then, when the silent chain 2 is driven by the sprocket 7 and is
traveling in the transverse-runout state, the engagement starting points
P3 and P4 of the respective front inner-flank surfaces 34 and 44 of the
middle and inner link plates 30 and 40 with the sprocket tooth 8 are set
at positions of avoiding the guide plate from contacting with the
sprocket tooth 8 before the front inner-flank surfaces 34 and 44 of the
respective link plates 30 and 40 starts to engage with the sprocket tooth
8, i.e., at position where they do not contact before the front
inner-flank surfaces 34 and 44 of the respective link plates 30 and 40
start to engage with the sprocket tooth 8, similarly to the case when the
silent chain 2 is located at the normal position.

[0072] Due to that, when the middle and inner link plates 30 and 40 starts
to engage with the sprocket tooth 8, the middle and inner link plates 30
and 40 contact with the sprocket tooth 8 always prior to the guide plates
10.

[0073] Then, the guide plate 10 is formed into such a shape that the
engagement starting points 23 and 24 are located at the positions of
avoiding the guide plate 10 from contacting with the sprocket 7 before
the respective link plates 30 and 40 start to engage with the sprocket
tooth 8, i.e., at the positions where the guide plates 10 do not contact
with the sprocket 7 before the respective link plates 30 and 40 start to
engage with the sprocket tooth 8.

[0074] Specifically, when the middle link plate 30 starts to engage with
the sprocket tooth 8 as shown in FIG. 3(a), the guide plate 10 has a
shape of avoiding the inner end surface 23 and the both inner side end
surfaces 24 and 25 from contacting with the sprocket tooth 8a before the
front inner-flank surface 34 of the middle link plate 30 starts to engage
with the sprocket tooth 8a in the transverse-runout state.

[0075] Due to that, the inner outline face 22 is located outwardly in the
radial direction more than the engagement starting point P3 in the whole
thereof including the inner end surface 23 before the front inner-flank
surface 34 starts to engage with the sprocket 7.

[0076] Then, when the guide plate 10 has an overlap portion 17 overlapping
with the sprocket tooth 8 in the side view as shown in FIG. 3(a), the
shape of the inner end surface 23 is set so that the sprocket tooth 8 is
located within the distance W by the overlap portion 17 even when the
chain is in the transverse-runout state in order to avoid the inner end
surface 23 from contacting with the sprocket tooth 8a before the front
inner-flank surface 34 starts to engage with the sprocket tooth 8a (see
FIG. 3(b)).

[0077] It is noted that as another example, the guide plate 10 may be
formed into a shape so that the entire guide plate 10 does not overlap
with the sprocket tooth 8 in the side view before the middle link plate
30 starts to engage with the sprocket tooth 8.

[0078] Still more, as shown in FIG. 4, the guide plate 10 may be formed
into a shape of avoiding the inner end surface 23 and the both inner side
end surfaces 24 and 25 from contacting with the sprocket tooth 8 before
the front inner-flank surface 44 of the inner link plate 40 starts to
engage with the sprocket tooth 8 in the transverse-runout state when the
inner link plate 40 of the non-guide row 4 starts to engage with the
sprocket tooth 8.

[0079] Due to that, the whole of the inner outline face 22 including the
rear inner side end surface 25 is located outwardly in the radial
direction more than the engagement starting point P4 and the entire guide
plate 10 does not overlap with the sprocket tooth 8 in the side view
(i.e., the entire guide plate 10 is located radially outside of the
sprocket tooth 8) before the inner-flank surface 44 starts to engage with
the sprocket tooth 8.

[0080] Furthermore, the guide plate 10 is formed into a shape of avoiding
the inner outline face 22 of the guide plate 10 from contacting with the
sprocket tooth 8b during a period from when the inner-flank surface 44 of
the inner link plate 40 starts to engage with the sprocket tooth 8b as
the engagement of the inner link plate 40 with the sprocket tooth 8
advances until when the both outer-flank surfaces 36 and 37 of the middle
link plate 30 located on the front side of, i.e., preceding to, the inner
link plate 40 contact respectively with the sprocket tooth 8c and 8b
located on the front side of the sprocket tooth 8a and seat on the
sprocket 7. That is, the guide plate 10 has a shape so that the guide
plate 10 does not overlap with the sprocket tooth 8 in the side view.

[0081] Therefore, the rear inner side end surface 25 is formed into the
shape of avoiding the rear inner side end surface 25 from contacting with
the sprocket tooth 8 during the period from when the inner link plate 40
starts to engage with the sprocket tooth 8 until when the middle link
plate 30 located on the front side of the inner link plate 40 seats on
the sprocket 7 or into the shape so that the rear inner side end surface
25 does not overlap with the sprocket tooth 8 in the side view.

[0082] Then, due to the positions of the engagement starting points P3 and
P4 described above and to the shape of the guide plate 10 with respect to
the sprocket tooth 8 described above, it becomes possible to prevent the
guide plate 10 from contacting with the sprocket tooth 8 before the
middle and inner link plates 30 and 40 even when the traveling silent
chain 2 is in the transverse-runout state during when the silent chain
transmission system 1 is operative.

[0083] Next, operations and effects of the embodiment configured as
described above will be explained.

[0084] In the silent chain transmission system 1 having the silent chain 2
and the sprocket 7 engaging with the silent chain 2, the engagement
starting points P3 and P4 of the middle and inner link plates 30 and 40
with the sprocket tooth 8 are set at the positions of avoiding the guide
plate 10 from contacting with the sprocket tooth 8 before the link plates
30 and 40 starts to engage with the sprocket tooth 8 when the silent
chain 2 is in the transverse-runout state as described above.

[0085] With this arrangement, because the engagement starting points P3
and P4 of the middle and inner link plates 30 and 40 with the sprocket
tooth 8 are located at the positions of avoiding the guide plates 10 from
contacting with the sprocket tooth 8 before the link plates 30 and 40
starts to engage with the sprocket tooth when the silent chain 2 is in
the transverse-runout state, it becomes possible to prevent the sprocket
teeth 8a and 8b from contacting with the guide plate 10 until when the
sprocket teeth start to engage with the inner-flank surfaces 34 and 44 of
the respective link plates 30 and 40 when the traveling silent chain 2
starts to engage with the sprocket teeth 8a and 8b in the
transverse-runout state.

[0086] As a result, it is possible to prevent the guide plate 10 from
contacting with the sprocket tooth 8 even when the silent chain 2 is in
the transverse-runout state before and after when the silent chain 2
starts to engage with the sprocket tooth 8. Then, it becomes possible to
keep the original engagement starting configuration of the sprocket tooth
8 that conforms to such a design concept that the respective link plates
30 and 40 of the silent chain 2 contact first with the sprocket tooth 8
in the same manner when the silent chain 2 travels on the normal position
and to improve the noise performance of the silent chain transmission
system 1 because it becomes possible to prevent the noise otherwise
caused by the contact of the guide plate 10 with the sprocket tooth 8
before starting the engagement.

[0087] The guide plate 10 is formed into the shape of avoiding the guide
plate 10 from contacting with the sprocket tooth 8 before the inner-flank
surface 34 of the middle link plate 30 starts to engage with the sprocket
tooth 8 and before the inner-flank surface 44 of the inner link plate 40
starts to engage with the sprocket tooth 8 in the transverse-runout
state.

[0088] With this arrangement, it becomes possible to realize the setting
of the engagement starting point P3 of the inner-flank surface 34 of the
middle link plate 30 with the sprocket tooth 8 and the engagement
starting point P4 of the inner-flank surface 44 of the inner link plate
40 with the sprocket tooth 8 at the positions of avoiding the guide plate
10 from contacting with the sprocket tooth 8 before the respective
inner-flank surfaces 34 and 44 starts to engage with the sprocket tooth 8
when the silent chain 2 is in the transverse-runout state with the simple
structure by using the guide plate 10 having the shape of avoiding the
guide plate 10 from contacting with the sprocket tooth 8 before the
respective inner-flank surfaces 34 and 44 starts to engage with the
sprocket tooth 8.

[0089] The abovementioned effect is also brought about when the guide
plate 10 is formed into the shape so that the guide plate 10 does not
overlap with the sprocket tooth 8 in the side view before the inner-flank
surface 34 of the middle link plate 30 starts to engage with the sprocket
tooth 8 in the transverse-runout state and so that the guide plate 10
does not overlap with the sprocket tooth 8 in the side view before the
inner-flank surface 44 of the inner link plate 40 starts to engage with
the sprocket tooth 8.

[0090] The guide plate 10 is also formed into the shape of avoiding the
guide plate 10 from contacting with the sprocket tooth 8 during the
period from when the inner-flank surface 44 of the inner link plate 40
starts to engage with the sprocket tooth 8b until when the both
outer-flank surfaces 36 and 37 of the middle link plate 30 seat on the
sprocket 7 when the silent chain 2 is in the transverse-runout state.

[0091] With this arrangement, in the inner flank engaging and outer flank
seating type silent chain 2, the guide plate 10 does not contact with the
sprocket tooth 8 until when the middle link plate 30 seats on the
sprocket 7 even after when the inner-flank surface 44 of the inner link
plate 40 starts to engage with the sprocket tooth 8b in the same manner
with the case when the inner-flank surface 44 of the inner link plate 40
starts to engage with the sprocket tooth 8b. As a result, because it is
possible to prevent the noise otherwise caused by the contact of the
guide plate 10 with the sprocket tooth 8 even after when the inner link
plate 40 starts to engage with the sprocket tooth 8, it is possible to
improve the noise performance of the silent chain transmission system 1
further.

[0092] Still more, it is possible to realize the non-contact state of the
guide plate 10 and the sprocket tooth 8 during the period after when the
inner link plate starts to engage with the sprocket 7 until when the
middle link plate 30 seats on the sprocket 7 by the simple structure by
using the guide plate 10 having the shape of avoiding the guide plate 10
from contacting with the sprocket tooth 8 during the period after when
the inner link plate 40 starts to engage with the sprocket 7 until when
the middle link plate 30 seats on the sprocket 7.

[0093] Furthermore, because the entire inner outline face 22 is located
outwardly in the radial direction more than the engagement starting
points P3 and P4, it becomes possible to downsize the guide plate 10 in
the radial direction and to lighten the guide plate 10. Still more,
because the guide plate 10 has the shape of avoiding the rear inner side
end surface 25 of the guide plate 10 from contacting with the sprocket
tooth 8 during the period after when the inner link plate 40 starts to
engage with the sprocket 7 until when the middle link plate 30 seats on
the sprocket 7, it becomes possible to downsize the guide plate 10 in the
radial direction further.

[0094] An example in which part of the abovementioned embodiment is
modified will be explained below centering on the modified part.

[0095] That is, the engagement starting point P3 or the engagement
starting point P4 of one of link plates of the middle and inner link
plates 30 and 40 may be set positions of avoiding the guide plate 10 from
contacting with the sprocket tooth 8 before one of the link plates starts
to engage with the sprocket tooth 8 when the silent chain 2 is in the
transverse-runout state. It is possible to reduce the noise otherwise
caused by the contact of the guide plate 10 with the sprocket tooth 8 as
compared to the technology of contacting the guide plate with the
sprocket tooth before the middle link plate and inner link plate starts
to engage with the sprocket tooth when the silent chain is in the
transverse-runout state also in this case.

[0096] It is noted that in a case when the sprocket 7 is a driven
sprocket, the engagement starting points P3 and P4 are located on the
rear inner-flank surfaces 35 and 45.